According to researchers, mass tests are not a “silver bullet” for managing SARS-CoV-2 transmission

Many European countries are suffering from a second wave of the 2019 coronavirus disease (COVID-19) pandemic. In many cases – like in the UK, Italy and Belgium – this has forced countries to lock again nationwide. While the Test-Trace-Isolate Approach remains the most effective way to control epidemic rebound after lockdown ends, there is much debate among experts about optimal methods for using tests.

Paris, France - November 13, 2020: Covid-19 rapid test medical tent in front of a pharmacy.  Photo credit: UlyssePixel / Shutterstock

Paris, France – November 13, 2020: Covid-19 rapid test medical tent in front of a pharmacy. Photo credit: UlyssePixel / Shutterstock

So far, the tests are mainly aimed at symptomatic people and contacts of positive cases. The increasing availability of new diagnostic tests enables mass testing to be viewed as a strategy. Mass tests help to test a large part of the population through a single campaign and to identify and isolate several infected people at the same time.

The development of rapid tests for the detection of SARS-CoV-2 has made it easier to conduct mass tests, as these tests provide results within 30 minutes compared to standard PCR tests, which take 1-2 days for results. Although the sensitivity of antigen tests in detecting SARS-CoV-2 does not match the PCR tests, the sensitivity threshold of the most sensitive antigen tests is sufficient to identify a large proportion of infectious people with very high virus levels. Even with these rapid antigen tests, mass testing is very difficult to implement and its effects have yet to be determined.

Using a mathematical model to assess the effects of mass testing during a SARS-CoV-2 rebound

A team of researchers from various French institutions recently used a mathematical model to assess the impact of mass testing on combating the SARS-CoV-2 epidemic. They assessed the possible impact of mass test campaigns in an epidemic rebound scenario at the end of the ongoing lockdown in the French metropolis. Your study was published on the pre-print server. medRxiv *.

The team used a SEEIR compartment model to describe the spread of SARS-CoV-2 in the French metropolis. They found that most people move within 4 compartments after infection. 1. Compartment E1, where they were exposed but not yet infectious, with an average duration of 4 days; 2. Compartment E2, where they are infectious and can transmit diseases but show no symptoms, with an average duration of 1 day; 3. Compartment I, where they are infectious and may be symptomatic, with an average duration of 3 days; and 4th compartment R, where they have recovered. This description indicates a generation time of around 7 days, which agrees with the existing data on SARS-CoV-2 transmission chains and virus shedding.

Mass tests are not a “silver bullet” that can replace other control measures

The results of their analysis suggest that in order to positively affect the epidemic dynamics, mass tests should be targeted at a large part of the population, should be repeated and rely on a rapid test with good sensitivity to identify all infectious individuals. The researchers also say their results emphasize that the strategy will only work if a large proportion of those who test positive are effectively isolated.

Our analysis suggests that in order to positively influence the epidemic dynamics, mass tests must appeal to a large part of the population, must be repeated and rely on a test with good sensitivity to identify infectious individuals. “

Using a simple mathematical model, this study highlighted the potential and limitations of mass testing as a strategy to combat the SARS-CoV-2 pandemic. A major limitation of mass testing is that at the beginning of the campaign, around half of infected people are still in the E1 latency period, during which they do not release enough viruses to perform positive tests. These undiscovered people become contagious after the campaign and fuel the epidemic again.

Based on the results, the researchers concluded that the conditions needed to combat a rapidly growing epidemic using mass testing seemed impossible to achieve. Mass tests should therefore not be seen as a panacea that can replace other control measures. According to the authors, even with established optimistic assumptions, mass testing is most relevant when epidemic growth is limited and only as part of a combination of interventions.

Mass testing should therefore not be viewed as a panacea that ensures that other control measures can be removed. “

* Important NOTE

medRxiv publishes preliminary scientific reports that are not peer-reviewed and should therefore not be considered conclusive, guide clinical practice / health-related behavior, or are treated as established information.

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